1. Field of the Invention
This invention relates to a silicon nitride sintered body having an improved oxidation resistance or wear resistance.
2. Related Art Statement
Silicon nitride sintered bodies are often used at their as-sintered or worked surfaces for gas turbine members and high temperature structural members. On the other hand, as disclosed in Japanese Patent laid open Nos. 60-161,383 and 60-200,882, the surface of the silicon nitride sintered body is covered with a coating of silicon nitride by a chemical vapor deposition (CVD) process to eliminate the surface defects and enhance the strength prior to the use.
In these silicon nitride sintered bodies constituting the above member at their as-sintered or worked surfaces, however, when used at high temperature, the oxidation resistance and the wear resistance are deteriorated as compared with the case of using at room temperatures. Therefore, when they are used as a gas turbine member or a high temperature structural member, the service life is considerably shortened.
Further, in the silicon nitride sintered body covered with the coating of silicon nitride by the CVD process, the coating of silicon nitride is destroyed by reacting with the sintered body thereby losing the effect of the coating formation.